Interpretive Summary: While feeding on plants, aphids inject saliva which aids in feeding, but is toxic to plant tissues. Comparing salivary composition among different aphid species could help identify which products are important for general aphid feeding, which products are specific among certain host associations, or which products cause specific damage to crops. We compared the saliva from five aphid species including three Diuraphis species (the Russian wheat aphid, the western wheat aphid, and D. mexicana), the greenbug, and the pea aphid. One salivary protein (alkaline phosphatase) was detected from the saliva of all five species and may have a universal role in aphid feeding. The three Diuraphis species, which cause visibly similar injury to grasses, shared nine protein products that were absent from the saliva of the other two species. The greenbug uses some of the same hosts as the Diuraphis species, but injury to hosts caused by greenbug feeding is visibly different from that caused by Diuraphis feeding. Only two protein products were common to the saliva of Diuraphis and the greenbug. Ten protein products were detected only from the saliva of the pea aphid, which feeds on different host plants than the three Diuraphis species and greenbug. Our comparisons of aphid saliva revealed marked similarities among species that cause similar injury on mutual hosts, fewer similarities among species that cause visibly different injury on mutual hosts, and little similarity among species that feed on unrelated hosts.

Technical Abstract:
Aphid (Hemiptera: Aphididae) saliva, when injected into host plants during feeding, causes physiological changes in hosts that facilitate aphid feeding and cause injury to plants. Comparing salivary constituents among aphid species could help identify which salivary products are universally important for general aphid feeding processes, which products are involved with specific host associations, or which products elicit visible injury to hosts. We compared the salivary proteins from five aphid species, namely, Diuraphis noxia Kurdjumov, D. tritici Gillette, D. mexicana Baker, Schizaphis graminum Rondani, and Acyrthosiphon pisum Harris. A 132-kDa protein was visualized from the saliva of all 5 species using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Alkaline phosphatase activity was detected from the saliva of all five species and may have a universal role in the feeding process of aphids. The Diuraphis species cause similar visible injury to grass hosts, and nine electrophoretic bands were unique to the saliva of these three species. S. graminum shares mutual hosts with the Diuraphis species, but visible injury to hosts caused by S. graminum feeding differs from that of Diuraphis feeding. Only two mutual electrophoretic bands were visualized in the saliva of Diuraphis and S. graminum. Ten unique products were detected from the saliva of A. pisum, which feeds on dicotyledonous hosts. Our comparisons of aphid salivary proteins revealed similarities among species which cause similar injury on mutual hosts, fewer similarities among species which cause different injury on mutual hosts, and little similarity among species which feed on unrelated hosts.